1. Field of the Invention
The present invention relates to treatment of a gas stream, such as an exhaust gas stream of an internal combustion engine.
2. Discussion of the Background
Particulates such as soot contained in exhaust gas discharged from internal combustion engines of vehicles such as buses and trucks, construction machines, and the like, for example, are harmful to the environment as well as humans. In turn, a variety of exhaust gas treating apparatuses have been developed that use a honeycomb structure made of porous ceramic as a filter for capturing particulates contained in the exhaust gas to purify the exhaust gas. Such an exhaust gas treating apparatus may be manufactured by arranging the surface of the honeycomb structure to carry a catalyst such as platinum. Also, certain exhaust treating apparatuses may be arranged to carry alkaline earth metals such as Ba to be used as a NOx absorbing agent for treating NOx under an oxidizing atmosphere in a lean burn engine or a diesel engine, for example.
It is noted that defects such as holes or scratches may be formed on the honeycomb structure during the manufacturing process of the honeycomb structure or the manufacturing process of the exhaust gas treating apparatus. Japanese Laid-Open Patent Publication No. 2005-144284 discloses a ceramic honeycomb structure having plural flow paths partitioned by plural partition walls and an outer wall that separates the flow paths from the exterior, wherein at least one defective portion corresponding to a hole with a width of 0.1 mm or more formed on the outer wall surface and connected to at least one of the flow paths is sealed with ceramic material. The entire contents of Japanese Laid-Open Patent Publication No. 2005-144284 are incorporated herein by reference.